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Basic Fiber Optics

A Brief Overview

Developed by Ted J. Pappas

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Fiber Optic Basics and the Cell Site

Fiber Optic Lines are strands of optically pure glass as tin as a human hair

In fact the light carrying

component of an optical

fiber is in the neighborhood

of 9 to 60 microns or 9 to

60 millionths of a meter in

diameter

Ted J. Pappas

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So Why are The Service Providers

Deploying Optical Fiber Up The Tower?

Less Expensive – Optical Fiber can be manufactured cheaper than equivalent lengths of copper Thinner – Optical Fibers can be drawn to smaller diameters than copper wires Higher Carrying Capacity – More fibers can be bundled into a given diameter and light weight Less Signal Degradation – The loss of signal in Fiber is less than in copper wires and can use lower power transmitters Light Signals – Unlike electrical signals in copper light signals from one fiber does not interfere with those other fibers in the same cable. NO INDUCTION.

Ted J. Pappas

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What is the Basic Structure of an Optical Fiber?

plastic jacket glass or plastic cladding fiber core

There are Three (3) Components

1. The Core

2. The Cladding

3. The Buffer / Jacket

Ted J. Pappas

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The Core is generally made of glass. The core is described as having

an index of refraction n1.

The core is surrounded by a layer of material called the Cladding.

Even though light will propagate along the fiber core without the layer

of cladding material, the cladding does perform some necessary

functions.

The cladding layer is made of a dielectric material with an index of

refraction n2. The cladding performs the following functions:

Reduces loss of light from the core into the surrounding air

Reduces scattering loss at the surface of the core

Protects the fiber from absorbing surface contaminants

Adds mechanical strength

Fiber Structure

Ted J. Pappas

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Types of Optical Fiber

Step-Index Multi-Mode fiber has a large Core (50-62.5 Microns)

composed completely of one type of glass.

Transmit infrared light at wavelengths of 850 to 1300 nm from light-emitting

diodes (LEDs)

Light travels in straight lines in the fiber reflecting off of the core/cladding

boundary. Since each mode or angle of light travels a different path, a

pulse of light is dispersed while traveling through the fiber limiting its

bandwidth.

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Types of Optical Fiber

Graded-Index Multi-Mode fiber has a large Core (50-62.5 Microns)

composed completely of one type of glass. Transmit infrared light at

wavelengths of 850 to 1300 nm from light-emitting diodes (LEDs) Light travels faster in a lower index of refraction, the light will travel faster as it approaches the outside of the core. Likewise---light traveling in the center will move slower. A properly constructed index profile will compensate for the different path lengths of each mode, increasing bandwidth capacity by as much as 100 times over that of step index.

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Types of Optical Fiber

Single-Mode , or Monomode, fiber has small Cores (~9- Microns)

composed completely of one type of glass. Transmit infrared light at

wavelengths of 1300 to 1550 nm from Lasers.

Single Mode fiber shrinks the size of the core to a dimension of about six

times the wavelength of the fiber (microns in diameter). This causes the

light to travel in only one mode.

Modal dispersion disappears and the bandwidth of the fiber increases

tremendously over graded-index fiber. Less susceptible to signal loss.

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Fiber Optic Connectors

In the development of fiber optic technology

over the last 30 years, many companies and

individuals have invented the :better

mousetrap”---a fiber optic connector that was

lower loss, lower cost, or easier to terminate. In

all ~100 fiber optic connectors have been

introduced to the market place, but only a few

represent the majority of the market.

Most fiber optic cables are “plugs” or so-called

make connectors with a protruding ferrule that

holds the fibers in alignment.

The Ferrule may be ceramic or polymer or plastic

*****Don’t Forget The Ferrule Cap *****

Ted J. Pappas

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The ST Connector

The ST is probably still the most popular connector for multi-mode.

The prominent feature of the ST is similar to the BNC RF Connector.

It has a bayonet mount and a long ferrule. STs are spring-loaded so

you have to make sure they are seated properly

If you have high loss, reconnect them to see if it makes a difference

Ted J. Pappas

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The SC Connector The Ethernet Standard

The SC is a “snap-in” connector and is widely used for its

excellent performance. It is the standard connector for

Ethernet 802.3.

The connector is also available in duplex configuration

Ted J. Pappas

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The FC Connector

FC was one of the most popular single mode conductors for

many years. It screws on firmly, but you must make sure that

the “key” is aligned in the slot properly before tightening.

It has mostly been replaced by SSC and LC Connectors

Ted J. Pappas

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The LC Connector

The LC is a small form factor connector half the size of the SC. Come in Duplex Mode as well

Ted J. Pappas

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Fiber Bend Radius

Is there really a bend radius limit with optical cable?

YES

The minimum radius

that an optical fiber can

be bent without loss or

impairment. The radius

varies with different

cable designed but

follows a general rule

that is be no less than

15 times the cable

diameter

Ted J. Pappas

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Bending the fiber also causes attenuation. Bending loss is classified

according to the bend radius of curvature: microbend loss or macrobend

loss.

Microbends are small microscopic bends of the fiber axis that occur mainly

when a fiber is cabled. Macrobends are bends having a large radius of

curvature relative to the fiber diameter. Microbend and macrobend losses

are very important loss mechanisms. Fiber loss caused by microbending can

still occur even if the fiber is cabled correctly. During installation, if fibers are

bent too sharply, macrobend losses will occur.

Micro and Macro Bends

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No

Velcro or Tie-Wraps

Distribution to the light path causing signal loss or degradation

Ted J. Pappas

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Optical Cable Hoisting and Pulling

There are many derivatives of Kellums / Pulling

Grips and different lengths of the same grip to

ensure a consistent grip on the utility

Grip with “Shoulder” to protect the

leasing edge of the utility

Reinforced double and triple

weave and pulling eye

Rotating head that will move

when not under load to relieve

twist in the cable

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Kellums / Pulling Grip “ENGAGED’ Length

A “loose” grip will be as much as 50 percent shorter when fitted

onto the utility and larger diameter grips will get even shorter

than their received length.

Catalog Lengths list Engage Length when the Grip is fitted to the utility

Ted J. Pappas

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Don’t forget the LINE SWIVEL

The type of Line Swivel corresponds to pulling grip strength and

should be mounted in series to the grip to allow for rotation during

installation

Ted J. Pappas

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Fiber Optics Cable has a tensile load rating that defines the maximum vertical rise that a cable being hoisted can withstand without Additional Support

The Load, The Right Tool, The Vertical Rise

1/2 x maximum long-term tensile load) / cable weight

Prevent Optical Fiber Damage

Support Network Expansion Design

Ted J. Pappas

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Thank You